1. Field of the Invention
The present invention relates to an improved hand prosthesis or artifical hand.
2. Description of the Prior Art
French Pat. No. 73 25719 of the July 13, 1973 in the name of the applicant proposed an artifical hand which comprises a metal or plastic skeleton, with articulated phalanges, covered with molded rubber foam coated with a reinforced elastomer skin with, on its back part, traction springs which return the fingers into the open position and with, on its palmar portion, nylon threads which slide in flexible sheaths and are attached to the phalanges or top joints, the three phalanges of each finger (two for the thumb) being articulated together without lateral play for the thumb, the forefinger, the middle finger and with lateral play for the ring finger and the little finger, and the palm of the hand comprises a base piece, integral with a ball joint for orientating the wrist and forming two metacarpals for the thumb and the forefinger, and three metacarpals for the middle finger, the ring finger, the little finger, fixed resiliently to the base piece. Furthermore, the certificate of addition No. 74 23597 of the July 8 1974, to the above patent, describes among other things an improvement in which the thumb is lockable manually in several positions and pivots on an oblique gusset carried by the base piece, with a spring pawl and teeth providing the locking.
Of course the articulated phalange prosthesis known from this patent and certificate of addition has numerous advantages and, in particular, provides an artificial hand capable of very elaborate gripping, it has however a certain number of disadvantages which the applicant has sought to remedy. In fact, in the artifical hand of the prior art represented by these publications, some of the mechanical parts (traction springs) are associated with the dorsal or back part and others (the articulation threads); with the palmar part of the prosthesis. This forms a considerable disadvantage for manufacture, since the dorsal portion, the palmar portion and the mechanical parts of the prosthesis are manufactured separately then assembled together to form the prosthesis. This also forms a serious drawback in the case where, because of wear thereof or a malfunction, the mechanical parts of the prosthesis must be repaired or replaced. Since an operation on the prosthesis for repairing or replacing mechanical parts concerns both the dorsal and palmar portions of the prosthesis it is therefore complicated and expensive. In addition, in the known prosthesis, the fingers are integral with the base piece mentioned above, which forms the palm of the prosthesis so that if one of the fingers becomes defective and unusable, it is the whole of the mechanism which must be replaced.